1. Technical Field
The present invention relates to an orientation capability evaluating apparatus which evaluates orientation capability of an orientation film used for liquid crystal display elements.
2. Background Art
In recent years, liquid crystal displays have been in wide-spread use. In the liquid crystals used in a liquid crystal display element constituting the liquid crystal display apparatus, its orientation process is an indispensable technique. It becomes known that a state of the orientation processing is responsible for change in a display quality and a display error.
The recent study of the orientation mechanism has lead to research for realizing optimization of the state of the orientation.
As an alignment processing method or an orientation processing method, almost all of the currently-used liquid crystal elements utilize a substrate on which the orientation processing is perfomed, thereby, the orientation of liquid crystal molecules is controlled. In this specification, the terms orientation and alignment will be used interchangeably. As the orientation processing method for the substrate, the surface of polymer film is rubbed unidirectionally by rubbing cloth such as polyester cloth, and there is obtained the orientation film by properly processing so that an orientation vector thereof is oriented in a predetermined direction.
The above-mentioned method for rubbing the orientation film is suitable for mass production and is less costly, so that most of the liquid crystal display elements utilize the orientation film made in this method. However, though the procedure in the rubbing technique is rather simple, its decision making on a produdction basis is very difficult. In other words, the liquid crystal molecular orientation capability greatly changes depending on orientation film material, rubbing material, the number of rubbing operations, rubbing speed and so on. Thus, it is not easy to achieve a stable rubbing operation.
The liquid crystal molecular orientation capability for the substrate can not be evaluated until after the liquid crystal display element is actually assembled utilizing the substrate on which the rubbing techinique is performed, and then its display characteristic is tested, in the conventional practice.
In Japanese KOKAI 64-35419, tried is the orientation capability evaluation by absorbance utilizing linearly polarized infrared light. However, in this evaluation method, the glass absorbs the infrared light, so that measurement can not be carried out in a finished product utilizing a glass substrate. Therefore, it is necessary to make an orientation film by utilizing a test-purpose substrate such as calcium fluoride that transmits the infrared. The finished product means a commodity produced after a patterning process. In other words, a dummy or a test sample must be used in order for the evaluation purpose in the conventional practice.
Moreover, the direction of the sample substrate need be changed in order to change a polarizing direction, and the measurement is carried out through a polarizer. Thus, it is difficult or almost impossible to evaluate the orientation film during the production process.
Accordingly, even though there occurs a rubbing defect of the orientation film during the production process of the liquid crystal display elements in a factory line, such defect can not be found until the liquid crystal display is actually assembled, thus causing to deteriorate a production yield. Moreover, it is difficult to decide on a definite condition for rubbing, so that it is difficult to obtain the orientation film whose orientation is stable.